Does prolonged exercise alter diet-induced thermogenesis?

Diet-induced thermogenesis (DIT) is mainly an insulin-mediated response and the result of fat and glycogen synthesis. We investigated DIT at rest and after exercise to clarify the mechanism of exercise-induced changes in DIT in 6 healthy men (mean age 36 +/- 16 years). Subjects exercised for 1 h at 58% of maximal O2 consumption on a bicycle ergometer and then rested for 8 h sitting in a comfortable chair (exercise experiment). On a different day, subjects rested for 8 h without preceding exercising (non-exercise experiment). At 12.30 h, the subjects were given their second meal. DIT to individual meal did not differ significantly between the exercise and non-exercise days. Increased insulin sensitivity and increased free fatty acid oxidation by exercise may facilitate the conversion of glucose to glycogen in muscle. On the other hand, insulin secretion expressed as the ratio of plasma levels of insulin to glucose after the meal was significantly decreased in the exercise experiment (p < 0.05). Study of heart rate variability showed that sympathetic tone, a primary hormonal determinant of glucose metabolism during exercise, was increased and parasympathetic tone was decreased during the recovery period in the exercise experiment (p < 0.05). These findings suggest that changes in DIT are affected by many factors and may be related to the balance between these counteracting factors.